1. Field of the Invention
The present invention relates to a liquid temperature regulator for feeding heat-loaded liquid while keeping its temperature constant and more particularly to a temperature regulator for a heat transfer medium used in machining apparatus and equipment.
2. Description of the Prior Art
With the development of lasers and semiconductors in recent years parts related with lasers and semiconductors are now required to be manufactured with very high machining precision. The allowable machining error is in the order of a micron and preferably in the order of a sub-micron. For such high precision machining as generally called "super precision machining", the heat transfer medium also should be very precisely temperature-controlled with a temperature precision of .+-.0.1.degree.-0.001.degree. C. The term "heat transfer medium" as used herein includes lubricating oil for static pressure bearing, grinding oil and oil and water in a shower system.
The prior art control method hitherto used to control the temperature of such heat transfer medium within the variation range of .+-.0.1.degree.-0.001.degree. C. is to arrange heat exchangers in a series of stages and sequentially turn on and off the heat exchangers. In this prior art system the temperature wave is attenuated gradually and repeatedly through many heat exchanger stages. Obviously the whole volume of the apparatus is increased by multiplying the number of the heat exchange stages. Furthermore, the multi-stage heat exchanger system is more easily affected by disturbances caused by air, radiant heat etc. as compared with a single-stage heat exchanger system.
As another type of prior art apparatus there is known a liquid temperature regulator as shown in FIG. 1 of the accompanying drawings.
In FIG. 1, a liquid tank 10 contains a kind of liquid 20 whose temperature is to be controlled. The liquid 20 is fed into the tank through an inlet tube 30 and the temperature-controlled liquid 20 is fed out from the tank through an inlet tube 40 using a pump 41. In the regulator there is provided also a refrigeration cycle which includes a compressor 51, a condenser 52, a capillary tube 53, an evaporator 54 and, if necessary, an accumulator 55. The evaporator 54 is disposed in the liquid 20. The temperature of the liquid 20 is detected by a thermistor 61 connected to a temperature controller 60. The temperature controller 60 controls ON-OFF of the compressor 51 in accordance with the detected liquid temperature. When the temperature of the liquid 20 is higher than a predetermined value, the controller turns the compressor on. If lower than the pre-determined value, the controller turns the compressor off. By repeating ON-OFF operation in this manner, the liquid temperature control is effected. However, this temperature regulator according to the prior art involves the following problem:
Firstly, the temperature waveform in the prior art apparatus has a large amplitude. Secondly, the waveform contains a large amount of high frequency component. The waveform is shown in FIG. 2 which is a temperature-time characteristic curve of the liquid temperature measured at a point near the outlet tube 40 in the liquid tank 10 or at a point within the outlet tube 40.
The large amplitude of the waveform of the liquid temperature is attributable to the fact that ON-OFF time of the compressor 51 is long. The reason why such a long ON-OFF time is requried for the compressor 51 is that otherwise the useful life of the compressor is remarkably shortened by it.